Conventional active source absorption spectroscopy systems for analyzing gases, such as CO2, CH4, O2, etc. implement collocated transmitter and receiver components and, as such, require a short path length or reflections to return transmitted signals to the source location. Over long distances, the transmitted signals are reflected off mirrors or the ground to effect the return of the signal to the collocated receiver. Scattered returns from aerosol constituents or particles in these systems give rise to an additive error from backscattered radiation. This error effectively reduces the measured absorption, since the backscattered return completes only a partial path through the medium being analyzed. Additionally, if the reflector used is diffuse, large range-squared losses in the system result, prohibiting long-range implementation of the overall system.
In light of the shortcomings of these and other techniques, the need has been felt for a technique to measure constituents in a medium or the atmosphere so that partial path scattered return is ignored and to reduce transmission power losses where only diffuse targets exist for reflecting transmitted radiation.